ACCOxMMODATION 



411 



from the posterior face of the lens, which, being convex 

 backwards, is, of course, concave forwards, and acts as a 

 concave mirror (Fig. 130, A). 



Suppose the eye to be steadily fixed on a distant object, 

 and then adjusted to a near one in the same line of vision, 

 the position of the eyeball remaining unchanged. Then 

 the upright image reflected from the surface of the cornea, 

 and the inverted image from the back of the lens, will 

 remain unchanged, though it is demonstrable that their 

 size or apparent position must change if either the cornea, 

 or the back of the lens, alter either their form or their 



Fio. 131.— The Changes in the Lens in Accommodation. 



A, adjusted for distant ; B, for near objects. 



e, cornea ; con. conjunctiva ; scl. sclerotic ; cA. choroid ; c.p, ciliai-y 



process ; c.vi, ciliary muscle ; s.l, snspensory ligament. 



position. But the second upright image, that reflected by 

 the front face of the lens, does change both its size and 

 its position ; it comes forward and grows smaller (Fig. 

 130, B), proving that the front face of the lens has 

 become more convex. The change of form of the lens is, 

 in fact, that represented in Fig. 131. 



For purposes of accurate experiment it is better to 

 employ the images cast by ttvo small luminous points 

 placed one above the other. In this case three pairs of 

 images are seen by reflection ; and it is easier to observe 



